1. Field of the Invention
The present invention relates to the preparation of cyclic ketones, and, more especially, to the preparation of cyclic ketones from dicarboxylic acids.
The present invention more particularly relates to the preparation of cyclopentanone from adipic acid and 2,2-dimethylcyclopentanone from 2,2-demethladipic acid.
2. Description of the Prior Art
GB-A-615,543 describes the preparation of cyclopentanone by heating adipic acid in the presence of manganese carbonate or oxide. The yield obtained in respect of cyclopentanone, when the cyclization reaction is carried out at 280.degree. C., is excellent, on the order of 90%. However, this process is not completely satisfactory, as it is not possible to increase the level of cyclopentanone productivity. Indeed, to maintain the aforenoted levels of yield, it is necessary to limit the feedstream flow rates of adipic acid to about 0.7 kg/h per kilogram of catalyst. The feedstream flow rate could be increased by raising the reaction temperature.
Although the temperature indicated in GB-A-615,543 is said to range from 280.degree. C. to 350.degree. C., it is very difficult from an industrial standpoint to maintain a temperature of higher than 320.degree. C. without using complex apparatus or special, expensive heat transfer fluids. In addition, it is very difficult, if not impossible, to maintain such a temperature homogeneous in the viscous medium which is constituted by the liquid adipic acid and the manganese-based catalyst. Too, other than the difficulties indicated above, risks are presented of the deposit of polymeric substrates on the reactor walls ("lining") which are difficult to remove.
Another process for the preparation of cyclopentanone via cyclization of adipic acid, in the presence of a magnesium oxide catalyst, is described in U.S. Pat. No. 2,612,524. This particular process also requires a high temperature, ranging from 300.degree. C. to 350.degree. C.